chris hall monash centre for synchrotron science monash university, melbourne, australia
TRANSCRIPT
Chris Hall
Monash Centre for Synchrotron Science
Monash University, Melbourne, Australia.
Imaging small things Light microscopy
limited by penetrationLimited by wavelength (100s nm)
Electron microscopyHas to be done under vacuumExquisite resolution (0.2 nm)
X-ray microscopyDifficult to focus the x-rays15 nm is a very good resolution
Crystallography and coherent diffractive imaging (CXDI) X-ray crystallography
Details down to 0.1 nm…but only with crystals.
CXDI - Microscopy without lensesUse the coherence of the illuminating light to
obtain structural information.All the advantages of x-ray microscopy, but
much higher resolution (<10 nm)
The Goals of CXDI Imaging single (large) proteins Eventually use an x-ray free
electron laser Collect an image of the sample
(protein)…before it is blown apart.
More modest goals…small biological entities (cells).
70 nm
CXDI …how does it work?Axioms:
If the waves incident on the object are plane waves. Then in the far field, after interacting with the object the wave represents a Fourier Transform of the object.
To get back to an image of the object you simply need to perform an inverse Fourier transform.
In light optics the lens does this.
Detection and reconstruction If we can detect the complex far field wave
we can do the FT-1 with a computer. The problem is that our detectors only
detects intensity. No phase information is measured directly.
However, the phase can be estimated then refined by iteration.
Fourier transforms
Frequency
Intensity
F
Phase
Gershberg-Saxton (and family)
CXDI for real
J. Miao, K. O. Hodgson, T. Ishikawa, C. A. Larabell, M. A. LeGros and Y. Nishino, Proceedings of National Academy of Science of the USA 100, 110-112 (2003)
Fresnel CXDI
Fresnel CDI
Where will it happen
APS, Illinois, USA AS, Victoria, Australia
So, what are the current detector requirements?
In the geometry used now:
Energy range for > 50% DQE = 0.5 – 4 keVDynamic range in image (noise to saturation) >107
Pixel size ideally < 25 mPixel number >1024 x 1024Maximum local count rate 104 per pix per second
Trade studyCriterion Essential Desirable
1 Dynamic range 104 107
2 Pixelation 2048 x 2048 >4096 x >4096
3 Pixel Size <100 m < 50 m
4 Energy Range 0.5 keV to 3 keV 0.5 keV to 3 keV
5 Detective Quantum Efficiency
10% 50%
6 Rate Capability > 104 / pixel/ second > 106 / pixel/ second
7 Frame rate 1 Hz 1 kHz
8 Vacuum compatibility
10-4 bar 10-6 bar
9 Dead time fraction 10% 1%
10 Parallax error < 1 pixel at 20 degrees
11 Gaps in FOV Acceptable None
Commercially available detectors Easy option, but… Not designed for our purposes
XFEL pulse structure100 msecs 100 msecs
600 secs
Up to 30,000 pulses
100 fsecs104 photons, incident on the sample
99.4 msecs
Thank you for your attention
Thanks to my colleagues at MCSS and the CXSProf. Rob Lewis (MCSS)Prof. Keith Nugent (Melbourne University)Prof. Andrew Peele (La Trobe University)Dr. Garth Williams (Melbourne University)Dr. Mark Pfeiffer (La Trobe University)Evan Curwood (Monash University)Mr. Andrew Berry (Monash University)Dr. Wilfred Fullagar (Monash University)
The Australian Research Council fund theCentre of Excellence in Coherent X-ray Science.
Results so far
Gold blobs on Si3N4 substrate
Specifications for the CXS End Station apparatus Includes a 4 axis laser Doppler
displacement meter which provides:Positioning of sample w.r.t beam of 30 nmResolution in closed loop feedback of 0.2
nm=>Stability of sample w.r.t. beam of 2 nm